Molecular mechanisms of MOMP. The proposed models of MOMP leading to cytochrome c release are represented. (i) Bax pore. Bax or Bak forms a pore in the MOM after activation by a BH3-only protein such as Bid. (ii) PT pore opening. Opening of the PT pore allows an influx of water and ions into the matrix, causing matrix swelling; this leads to rupture of the MOM, releasing IMS proteins such as cytochrome c. MIM, mitochondrial inner membrane; PBR, peripheral benzodiazepine receptor.